The authors demonstrate a new technique for high sensitivity gas permeation measurements by integrating mass spectrometry with programed accumulation, detection, and evacuation of permeant. After passing through the film of interest, the gas permeant is captured and accumulated in an isolated ultrahigh vacuum (UHV) volume. The permeant is then allowed to enter an adjacent residual gas analyzer (RGA) and the resulting partial pressure increase is correlated with the steady state permeation rate. Calibrated results are given for helium and argon permeation through polymer films. The measured detection limits of the system are 1.8 X 10(-4) cm(3)/m(2) day for helium and 2.5 X 10(-4) cm(3)/m(2) day for argon. Both values are several orders of magnitude lower than what is available from commercial instruments or similar RGA-based instruments. Potential applications of this technique include measurement of oxygen and water vapor permeation with sensitivities required for assessment of ultrabarrier coatings. (c) 2007 American Vacuum Society.